This enables the newly introduced text-relative kallsyms support when
building 64-bit targets. This cuts the size of the kallsyms address
table in half, reducing the memory footprint of the kernel .rodata
section by about 400 KB for a KALLSYMS_ALL build, and about 100 KB
reduction in compressed size. (with CONFIG_RELOCATABLE=y)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
I tested this with my Ubuntu Wily box's config-4.2.0-23-generic, and
got the following results:
BEFORE:
=======
$ size vmlinux
text data bss dec hex filename
12972949 2213240 1482752 16668941 fe590d vmlinux
$ readelf -S .tmp_kallsyms2.o |less
There are 9 section headers, starting at offset 0x3e0788:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
...
[ 4] .rodata PROGBITS 0000000000000000 00000040
00000000001c7738 0000000000000000 A 0 0 8
[ 5] .rela.rodata RELA 0000000000000000 001c7950
0000000000218e38 0000000000000018 I 7 4 8
[ 6] .shstrtab STRTAB 0000000000000000 001c7778
0000000000000039 0000000000000000 0 0 1
$ ls -l arch/x86/boot/bzImage
-rw-rw-r-- 1 ard ard 6893168 Jan 20 09:36 arch/x86/boot/bzImage
AFTER:
======
$ size vmlinux
text data bss dec hex filename
12604501 2213240 1482752 16300493 f8b9cd vmlinux
$ readelf -S .tmp_kallsyms2.o |less
There are 8 section headers, starting at offset 0x16dd10:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
...
[ 4] .rodata PROGBITS 0000000000000000 00000040
000000000016db20 0000000000000000 A 0 0 8
[ 5] .shstrtab STRTAB 0000000000000000 0016db60
0000000000000034 0000000000000000 0 0 1
...
$ ls -l arch/x86/boot/bzImage
-rw-rw-r-- 1 ard ard 6790224 Jan 19 22:24 arch/x86/boot/bzImage
---
arch/x86/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4a10ba9e95da..180a94bda8d4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -142,6 +142,7 @@ config X86
select HAVE_UNSTABLE_SCHED_CLOCK
select HAVE_USER_RETURN_NOTIFIER
select IRQ_FORCED_THREADING
+ select KALLSYMS_TEXT_RELATIVE if X86_64
select MODULES_USE_ELF_RELA if X86_64
select MODULES_USE_ELF_REL if X86_32
select OLD_SIGACTION if X86_32
--
2.5.0
--
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